Industrial Stormwater FAQ

Industrial Stormwater Frequently Asked Questions

What is my "COC"?
What if I close my facility and have to rescind the stormwater permit?
What is a "No Exposure"?
What are stormwater benchmarks and how are they calculated?
Why are stormwater benchmarks different from the Water Quality Standards?
Do I need a certified lab to analyze my stormwater samples?  What about pH?
My permit requires analysis for "Non-polar Oil & Grease / TPH by Method 1664 (SGT-HEM)."  Is that more than one test?
If my facility uses more than 55 ga//month of motor oil BUT performs all vehicle maintenance indoors, do we still have to monitor VMA parameters in the permit?
If I take "extra" samples, do I have to send the results to DEMLR with my regular DMR data?
Can mobile car washing operations discharge wash water to storm drains?
What would a facility do if they have multiple outfalls, but each stormwater outfall is associated with industrial activity classified under different general permits? Would they apply for coverage under each applicable general permit, or would they have to get an individual permit?

What is my "COC"?

This refers to your "Certificate of Coverage."  The COC is the documentation showing the facility is covered under one of our General Permits.  The General Permit is the same for all facilities covered by that permit.  The COC issued to the facility contains a unique COC number, site location, receiving waters (for NPDES permits), and sometimes details about authorized discharges.  For example, a facility covered under NPDES General Permit NCG030000 may have a COC No. NCG030777.

What if I close my facility and have to rescind the stormwater permit?

You must send a letter to DEMLR Stormwater Permitting staff to request recission.  You should send the letter to the attention of the DEMLR Stormwater Permitting Program, and you must specify the individual permit or COC number.  You may also use the Rescission Form on the NPDES Stormwater Section of our website ('Miscellaneous Forms').  Please note that we coordinate with the Regional Office to process the request, which can take 1-2 months.

What is a "No-Exposure"?

Facilities with stormwater discharges "associated with industrial activity" may be excluded from permit coverage if industrial materials and operations are not exposed to stormwater.  For more information, see the No Exposure section of our website

What are stormwater benchmarks and how are they calculated?

Benchmarks are numerical action levels for pollutants that may be present in industrial stormwater.  All NPDES Stormwater Industrial permits include a table that lists the parameters that an industrial facility is required to monitor and the benchmarks associated with each parameter.  Benchmarks are different from effluent limits because a stormwater discharge concentration that exceeds a benchmark concentration in the permit table is not a violation of a stormwater permit.  However, a permittee who fails to conduct the required investigations to determine the source of the exceedance or who fails to take the required actions to correct the exceedance is in violation of his/her stormwater permit. 

The Stormwater Program provides benchmarks with assistance from the Division of Water Resources’ Classifications and Standards, Rules Review Branch.  These DWR staff members use data from multiple sources to develop stormwater benchmarks, including EPA’s National Recommended Water Quality Criteria, the National Primary Drinking Water Regulation (40 CFR 141.11), and NC Surface Water Quality Standards (15A NCAC 02B .0200). When these resources do not contain information for a particular pollutant of concern, benchmarks are calculated per 15A NCAC 2B .0200 using peer-reviewed toxicity data.  

Another important point about benchmarks is that they are set for each pollutant based on the effects on aquatic life from acute (short-term) exposure to the pollutant.  The effects that are considered include both mortality and impairment to biological functions like feeding, movement, and predation.  Acute rather than long-term impacts of pollutants are considered because rainfall events occur sporadically.    

Why are stormwater benchmarks different from Water Quality Standards? 

There are a few reasons for the differences between stormwater benchmarks and water quality standards: 

  • Benchmarks are based on acute (short-term) rather than chronic (long-term) pollutant levels. 

  • Different technical sources may be used to develop a stormwater benchmark than a water quality standard. 

  • Benchmarks for metals are based on total pollutant concentrations (the sample is not filtered before analysis), and (most) water quality metals standards are based on dissolved pollutant concentrations (the sample is filtered before analysis).   

Do stormwater monitoring samples have to be analyzed by a certified lab or entity?  What about pH, which has to be done in the field?

Stormwater Discharges:  North Carolina certification procedures do not apply to stormwater-only discharges at this time.  However, any monitoring of discharges under an NPDES permit (including stormwater) must be conducted in accordance to test procedures approved under federal regulations in 40 CFR §136.  This includes measuring pH properly within the 15-minute hold time.  All labs certified by North Carolina perform analyses in accordance with federal procedures.  So, even if your facility is not classified as a Water Pollution Control System, using a North Carolina certified lab is often the easiest way to comply with NPDES Program requirements.  A list of North Carolina certified labs can be found here.

Wastewater Discharges:  North Carolina certification procedures apply to wastewater discharges originating from Water Pollution Control Systems defined under T15A NCAC 8G .0300 and classified by the Technical Assistance and Certification Unit.  However, wastewater treatment facilities at most mines and ready-mixed concrete plants under General Permits NCG020000 and NCG140000 are not classified at this time.  Because state Operator and Laboratory Certification programs currently do not address these treatment facilities, there are no certification requirements for entities performing wastewater sample analysis (including field measurements like pH) at these sites right now, unless an exception is classified by the TACU.  Whether certified or not, discharge monitoring under an NPDES permit must be conducted in accordance to test procedures under 40 CFR §136.

My permit requires analysis for"Non-polar Oil & Grease/TPH by Method 1664 (SGT-HEM)." Is that more than one test?

No.  There has been confusion over this parameter in recent permits (mainly for vehicle maintenance monitoring), and we want to clear it up.  This description refers to ONE test:  Non-polar Oil &Grease using EPA Method 1664 with the silica gel treatment step, in addition to hexane extraction (not JUST HEM).  This gravimetric test method is an alternative way of estimating Total Petroleum Hydrocarbons (TPH), without using the more expensive gas chromatographic analysis.  This parameter does not refer to TPH analysis by gas chromatograph.  Future permits and DMR forms will be updated with language to avoid confusion about the term.  [Please note that currently labs in NC are being certified for Revision B to that Method under 40 CFR 136.]

If I take "extra" samples, do I have to send the results to DEMLR with my regular DMR data? 

Not unless conditions in your permit require you to.  Either way, you must maintain records of those results for at least five (5) years and provide them to DEMLR if requested (for example, by an inspector).  This obligation is in the "Records Retention" requirements found in the boiler plate sections of your permit.  Future standard permit requirements may explicitly require these data be reported. 

If your permit requires monitoring under a tiered-response structure tied to benchmark values, "extra" samples within the same monitoring period that exceed stormwater benchmark concentrations do not count as exceedances. 

Can mobile car washing operations discharge pressure wash water to storm drains without a permit?

No.  Vehicle pressure washing wash water is a wastewater, and discharge to surface waters through storm drains is not authorized by any NPDES stormwater permit.  You should check with your local government, as some may require a permit.  This fact sheet has additional details and information.  (Also see the NPDES Wastewater Guidance website.)

If my facility uses more than 55 gal/month of motor oil BUT performs all vehicle maintenance indoors, do we still have to monitor VMA parameters in the permit?

Probably.  Even when all maintenance is performed inside, the NPDES program considers parking lots used to store vehicles prior to maintenance as a component of the vehicle maintenance activity (VMA).  The facility must still monitor any outfalls draining those areas for VMA-related parameters if the parking area for these vehicles is exposed.

If all vehicles awaiting maintenance are not stored outside or otherwise exposed to stormwater, EPA guidance is not clear about whether monitoring applies when the minimum motor oil usage (indoors) is exceeded.  NC's NPDES Stormwater Program interprets current permit conditions to allow permittees to forgo VMA monitoring as long as no vehicle maintenance materials, maintenance activities, or vehicles are exposed in any drainage area.

What would a facility do if they have multiple outfalls, but each stormwater outfall is associated with industrial activity classified under different general permits? Would they apply for coverage under each applicable general permit, or would they have to get an individual permit?

It depends.  If their primary activity (or what constitutes the most exposure potential) is associated with one General Permit, and the monitoring requirements in that GP were sufficient enough to cover other outfalls with different types of industrial activity (i.e., the potential pollutants are covered in the GP we’re considering anyway), then we just cover the facility under the one General Permit.  If the activities really are diverse enough that the one General Permit is adequate, we’d have to take them the individual permit route.  This is a lot more involved for the permittee, we understand, but unfortunately, we don’t have a Program set up the same way as the EPA Multi-Sector permit, which requires facilities to follow every portion of the permit that pertains to their activities.